External antenna for cell phone
 

Does anyone know how to make an external antenna for a cellular phone? The Wife's office is in a place where the cell signal is too weak to talk, only sometimes she can text. I'd like to make an external antenna for her to hang in her office to plug into when she's at her desk.
I've googled around, but nothing of the simple wire loop design:( If it's any help, her phone is a Nokia.

Thanks:)

Your frequencies are different than ours so go here to get the lengths you need Antenna Elmer

I cant find the website but you will need to get the connector for the end of the phone, it should be a SMA, then adapt to the coax cable.
Next get 2 3/4" pvc pipe caps and about 2 foot of pvc pipe.
The 14ga copper wire antenna will get soldered to the center of a coax connector that gets threaded into 1 PVC cap.
measure 1/4 wavelength, bend 90deg, make a loop just smaller than the inside of the pipe, then 90 deg bend straight again. Measure 5/8 wavelength and cut.
Encase in pvc pipe to protect and youre done.
Similar antennas are made for wifi reception. Sorry I have to run or I'd google it.
I also made a double bi-quad that worked awesome

Found it !!!
Home-brew Compact 6dBi Collinear Antenna
Double Biquad Antenna
Much clearer with Marty's pictures.
Dont forget, the lengths will be a few mm different.